Book/Report

FZJ-2019-03750

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Untersuchung der Transporteigenschaften von SNS-Josephson-Kontakten, hergestellt durch die lokale Implantation von Sauerstoff

Kahlmann, F. (Corresponding author)FZJ*

1998
Forschungszentrum Jülich, Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/22411

Report No.: Juel-3545

Abstract: In this work the transport properties of SNS Josephson junctions fabricated by local oxygen implantation at 200 keV in YBa$_{2}$Cu$_{3}$O$_{7_x}$ are investigated. A sub-$\mu$m masking technology was used to restrict the spatial extent of the implanted region in the lateral direction to 50 nm. It is demonstrated for the first time that this technique could be used to fabricate Josephson junctions with homogeneous barrier properties. The improved junction properties are attributed to a post-implantation annealing step at 500°C for 10 min. in an oxygen atmosphere. A detailed study of the electrical transport properties and the crystal structure of oxygen implanted YBa$_{2}$Cu$_{3}$O$_{7_x}$ thin films serves as a basis for the fabrication process of the Josephson junctions. It is found that the irradiation of YBa$_{2}$Cu$_{3}$O$_{7_x}$ with oxygen at an energy of 200 keV leads to a linear decrease of the critical temperature T$_{c}$ and a quadratic increase of the specific resistance $\rho$ with increasing implantation dose $\Phi$. Annealing the implanted samples at 500°C for 10 min. in an oxygen atmosphere leads to an increase of the transition temperature and a decrease of the specific resistance but the initial values are not restored. This is due to the fact that annealing the implanted films at 500°C leads only to a partial reordering of the oxygen sublattice but does not influence defects formed on cation lattice sites. The analysis of implanted (spatial restricted by using a sub-$\mu$m mask) and subsequently annealed YBa$_{2}$Cu$_{3}$O$_{7_x}$ microbridges revealed that the implanted region has a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of <20 K. Close to the coupling temperature the critical current shows a nearly complete modulation in an applied magnetic field, indicating a homogeneous current distribution. Over the entire temperature range of Josephson coupling, which can be adjusted by varying the implantation dose, these junctions exhibit RSJ-like I-V characteristics with an additional excess current. The coupling temperature T$_{0}$ of the Josephson junctions, i.e. the upper limit of the temperature range, is determined by the implantation dose. The lower limit of the temperature range of RSJ-like Josephson junction behaviour is set by the finite transition temperature T$_{CN'}$-> 0 K of the barrier. The critical current I$_{c}$ of the junctions increases quasi exponentially with decreasing temperature. It is also demonstrated that the effective length L of the barrier region is temperature dependent (L $\propto$ (T - T$_{cN'}$)) and that this dominates the R$_{N}$(T) behaviour rather than the temperature dependence of the resistivity. Taking this into account it is shown that the I$_{c}$(T) behaviour can be very well described by conventional SNS proximity effect theory.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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